Various designs have already been proposed in the prior art for squirrel cages in short circuit rotors of asynchronous machines composed of copper and/or aluminum semifabricated pieces.
DE 10 2013 005 050 A1 discloses a short circuit rotor as well as a method for production of a short circuit rotor, wherein at least a portion of a shorting ring is composed of a disk stack, which is constructed of layers of disks with cavities through which the ends of the cage bars pass from the rotor lamination stack. The end faces of the disks of a shorting ring have at least one bevel along the outer periphery, which extends radially at least as far as the ends of the cage bars protruding from the rotor lamination stack. In other words, a freely accessible opening extends between neighboring disks as far as the level of the cage bars, so that the individual pieces can be joined together both electrically and mechanically.
DE 10 2014 013 684 A1 relates to a short circuit rotor for an asynchronous machine in which likewise several shorting rings arranged at the end faces of the rotor lamination stack are provided, having cavities into which the end regions of the rotor crosspieces protrude. It is proposed that the shorting rings each time are composed of at least two metal composite disks, which are made up of at least a first metal disk and a second metal disk joined to the latter by its surface and made from a different material.
One benefit of such a design is therefore the possibility of using different materials in the shorting rings, such as combining copper disks with copper alloy disks (CuCrZr or similar alloys) in order to boost the rotational speed capability and temperature stability of the asynchronous machine. The drawback, however, is that the welding process proposed therein alters the properties of alloyed copper and/or aluminum disks. In particular, due to the heating of these types of alloys to the welding temperature, they lose their properties in terms of strength and temperature stability. Assuming a rotor with relatively thin, easily fabricated individual disks, only a relatively small portion with the originally desired properties remains after the welding of the individual alloyed disks.
US 2014/0339950 A1 relates to a rotor arrangement with end caps, which should be welded by electron beam welding. This should produce improved electrical and mechanical properties in an arrangement of a lower weight. Specifically, a single end disk is described with axially noncontinuous grooves.
The drawback here is that the welding process occurs directly on the laminated rotor core and in the half-open grooves of the shorting disk. In this way, a very large input of heat into the laminated stack occurs, which may result in damage to the insulation. The molten welding pool can only be guided to a very limited degree and it readily flows.
DE 10 2013 202 557 A1 relates to a squirrel cage for a short circuit rotor and a manufacturing process for same. In this case, it is proposed to assemble the shorting rings from a connecting disk and a shorting disk, wherein the connecting disk has a plurality of cavities, in each of which is arranged a cage bar, so that the plurality of cage bars are mechanically fixed in relation to the connecting disk. The shorting disk lies immediately against the connecting disk in the axial direction. A materially-bonded connection between the cage bars and the connecting disk should be produced by means of a welded connection, a materially-bonded connection between the connecting disk and the shorting disk by means of a soldered connection.
Here as well, therefore, a welding occurs near the laminated rotor core, which may result in difficulties in regard to the insulation and the guidance of the molten welding pool. Especially in this embodiment, only the relatively thin connecting disk is welded to the shorting bars, preferably from an axial direction. This increases the risk of further flowing of the molten welding pool, since even with slight tolerance deviations or slight deviations in the welding parameters, the molten pool will flow into the joints between shorting bar and laminated stack or connecting disk and laminated stack. Hence, a large heat input into the laminated rotor core will occur. Another drawback is that the soldered connections of the shorting disk to the connecting disk result in lower strength and electrical conductivity as compared to welded connections. But since the shorting disk makes up the greater portion of the electrically conductive cross section of the ring, a relatively large centrifugal force acts on this ring.